Publius Helvius Pertinax (; 1 August 126 – 28 March 193) was Roman emperor for the first three months of 193. He succeeded Commodus to become the first emperor during the tumultuous Year of the Five Emperors.

Born the son of a freed slave, Pertinax became an officer in the army. He fought in the Roman–Parthian War of 161–166, where his success led him to be promoted to higher positions in both the military and political spheres. He achieved the rank of provincial governor and urban prefect. He was a member of the Roman Senate, serving at the same time as the historian Cassius Dio.

Following the death of Commodus, Pertinax was proclaimed emperor. He attempted to institute several reform measures, although the short duration of his reign as emperor prevented the success of those attempts. One of those reforms, the restoration of discipline among the Praetorian Guard, led to conflict that eventually culminated in Pertinax's assassination by the Guard. Pertinax would be deified by the emperor Septimius Severus. His historical reputation has largely been a positive one, in line with Cassius Dio's assessment.